This invention relates generally to inline inspection tools and techniques used to inspect piping and pipelines. More specifically, the invention relates to devices for controlling the speed of an inline inspection tool as the tool travels through a pipe.
Inline inspection tools and techniques are widely used in the piping and pipeline industry to provide information on the wall conditions of pipes. For example, as a magnetic flux leakage tool travels through the interior of the pipe, a magnetic circuit is created between the pipe wall and the tool. The magnetic flux saturates the wall and sensors located on the tool sense and collect data on flux leakage and interruptions in the magnetic circuit. The data are then analyzed to identify where metal loss has occurred due to corrosion, gouges, or other defects and determine the size of the metal loss at each location.
Many large diameter gas pipelines run at flow speeds that are outside the acceptable range for most inline inspection techniques. The underlying physics of many inline inspection techniques make adequate detection and sizing of anomalies at these higher speeds very challenging. For pipelines running at these high speeds, it would be desirable to allow some of the product to simply pass through the inspection tool to slow the speed of the tool without inhibiting the speed of the product flow. Unfortunately, the drive section of a typical inline inspection tool is designed to provide a tight seal, allowing very little bypass flow through the drive section.
Another concern with inline inspection tools is that there is a potential for the tool to become stalled or stuck within the pipeline. Pipeline debris and build-up may slow the tool below a desired minimum speed or may stop the tool entirely. To keep the tool moving, various passive and active speed control means have been developed. Passive control devices use pressure flow to actuate a primary bypass flow control valve that allows more or less product flow through the tool. Active control devices generally employ some combination of electrical, mechanical, or hydraulic means to actuate the bypass flow control valve. In some cases, however, the valve may fail while it is in the open position, causing the tool to stop moving.
Therefore, a drive section is needed that allows just enough bypass flow through the drive section to lower the tool speed yet still ensure that the tool successfully passes completely through the pipeline and provides a means for controlling bypass flow should the primary bypass flow control valve fail.